The present invention related generally to position sensors, and more particularly, to a rotary position sensor having potentiometer and a planetary gear set.
Rotary actuators have many applications. For example in the automotive industry, rotary actuators may be used in seat positioning mechanisms, mirror positioning mechanisms, and air conditioning and ventilation systems.
A relatively recent trend in automotive air conditioning systems has been the replacement of conventional, swinging flapper door valves with flexible film belts. A run of flexible film is rolled back and forth between a take up roller and a drive roller. A valve in the form of a window in the belt covers and uncovers an air passage within a housing of the system, allowing air through in direct proportion to the degree that the opening is uncovered. The result is more predictable control of airflow rates, as well as a potentially more compact system.
One advantage of the conventional, swinging flapper door is that it swings over less than a full turn, and it is therefore relatively easy to monitor its position. One known device is a potentiometer, in which a wiper that turns with the flapper door shaft wipes along an annular ring, back and forth, creating a changing resistance. The potentiometer works only over a full (or less than) 360 degrees, but that comports with the operation of the swinging flapper doors.
In contrast, the rollers that run the film belt must move through multiple turns. In order to use a potentiometer to measure the actuator position, a series of reduction gears may be used to step down the multiple turns of the belt roller into a single turn of the potentiometer. However, the potential exists for the potentiometer to become mis-aligned relative to the drive mechanism when the various gears are removed and replaced, such as during servicing. Thus misalignment will not be easily visible to the operator, but will throw off the position indicating function of the potentiometer.
One attempt to overcome this problem is described in U.S. patent application Ser. No. 09/652,246 filed Aug. 31, 2000 by inventor Donald John Enzinna. (now U.S. patent N/A). This system uses a set of reducing gears and a slip clutch for alignment of the system. However, this system does not allow the sensor to be manually calibrated.
Another problem with prior art sensors is that the sensor is relatively large.
The present invention is aimed at one or more of the problems as set forth above.
In one aspect of the present invention, a rotary position sensor for a rotating shaft is provided. The rotary position sensor includes a planetary gear set and a potentiometer. The planetary gear set is coupled to the shaft. The potentiometer is coupled to the rotating shaft and the planetary gear set and is adapted to measure a rotary position of the rotating shaft and responsively generate a position signal. The planetary gear set is adapted to reduce multiple rotations of the rotating shaft to less than a full rotation of the potentiometer.
In another aspect of the present invention, a rotary position sensor for a rotating shaft is provided. The rotating shaft is rotatably coupled to a housing. The rotary position sensor includes a planetary gear set and a potentiometer. The planetary gear set is coupled to the shaft and includes a pinion gear, a planet gear, and a ring gear. The pinion gear is coupled to the rotating shaft. The planet gear is engagingly coupled to the pinion gear. The ring gear is coupled to the housing and is engagingly coupled to the planet gear. The potentiometer is coupled to the rotating shaft and the planetary gear set and is adapted to measure a rotary position of the rotating shaft and responsively generate a position signal. The potentiometer includes a printed circuit board connected to the housing and having a PC board aperture. The potentiometer also includes a thick film resistor, a stop, and a wiper. The thick film resistor is located on a first side of the printed circuit board and has first and second ends and a generally circular shape. The stop is mounted to the printed circuit board between the first and second ends of the thick film resistor. The wiper is connected to an under side of the carrier and is in physical and electrical contact with the thick film resistor. The planetary gear set is adapted to reduce multiple rotations of the rotating shaft to less than a full rotation of the potentiometer.